This invention relates to a plasma processing apparatus. The invention relates also to an associated method of plasma processing.
Many industrial applications involve the use of a plasma to produce active species such as ions, electrons, atoms, molecules and radicals to meet a process requirement. Frequently, there is a need to operate at higher power densities in order to increase reaction speeds. One of the more commonly used types of plasma source in semiconductor or flat panel processing is the inductively coupled plasma (ICP) reactor. Typically, RF power is applied to an externally positioned antenna, coil or band resulting in inductive coupling of energy into the process chamber through a dielectric container or window. A suitable gas or gaseous mixture is introduced into the process chamber at a relatively low pressure and a gas discharge is produced. FIGS. 1a and b show examples of prior art ICP designs. Both FIGS. 1a and b show a process chamber 10 having a dielectric cylindrical body, RF feed points 12, 14 and a tuning capacitor 20. FIG. 1a shows a two turn ICP coil 16 which is externally positioned around the dielectric portion of the chamber 10. FIG. 1b shows a single turn ICP coil externally positioned around the dielectric region of the chamber 10. The removal of heat from this type of system can be a problem, owing to the relatively poor thermal conductivity of conventional dielectric materials. It is possible to use more advanced dielectric materials with improved thermal characteristics. An example of an advanced dielectric material is AlN. However, these advanced materials are costly and also they impose design limitations which limit their use in many applications.